9416652 Feher Various electron transfer steps in native and mutant reaction centers will be investigated. Two electron transfer steps will be addressed in detail: 1) the electron transfer rate from the primary quinone, QA to the secondary quinone, QB and ii) the charge recombination of QA and QB with the primary donor D+. The second problem deals with the protonation of the doubly reduced quinone. Q2- is buried inside the reaction center and is not accessible to protons from the outside. It is now generally believed that protons reach Q2- by a charge-relay mechanism involving protonatable residues. The problem is to identify the residues that constitute the proton transfer chain. This problem will be addressed by site- directed mutagenesis. Three residues Glu (L212), Arg (L213) and Ser (L223) have already been identified as being members of the proton transfer chain. In addition, the mechanism of proton transfer will be addressed by studying the coupling between electron and proton transfer and the role of electrostatics in the transfer. Theoretical calculations will be performed to complement, guide and explain the experimental results. %%% The goal of the research is to contribute toward an understanding of the primary processes in photosynthesis, i.e., the mechanism of conversion of electromagnetic energy into chemical free energy. The research will focus on the photosynthetic processes in purple bacteria (e.g. Rhodobacter sphaeroides). The findings will be of general interest and applicability to other biological systems and mechanisms, foremost to green plant photosynthesis and to other bioenergetic processes. The primary process of photosynthesis takes place in an integral membrane protein-pigment complex called the reaction center. Light produces a charge separation and initiates a set of electron transfer reactions resulting in the reduction of a terminal acceptor, which picks up two protons, and initiates the formation of the proton gradi ent that provides the driving force for the formation of high energy compounds. Thus, the main questions associated with the primary processes are associated with electron and proton transfers. ***
